This invention relates to an inductive angle sensor including: a stator element, having an exciting coil with a periodic AC voltage applied thereto and several receiving coils spaced from one another by a predetermined angle; a rotor element arranged to be movable relative to the stator element that affects an inductive coupling between the exciting coil and the receiving coils with an inductive coupling element as a function of the rotor element""s position relative to the stator element; and an evaluation circuit for determining positions of the rotor element from output signals of the receiving coils. This invention further concerns a process for evaluating the positions of such a rotor element.
In such an angle sensor, each receiving coil generates an output signal that depends substantially-sinusoidally on the position of the rotor element.
If a linear interrelationship is to be established between the output signals of the receiving coils and the position of the rotor element, signal processing becomes quite expensive, or measuring accuracy is reduced.
It is an object of this invention to provide an inductive angle sensor that, in an uncomplicated manner, generates a sensor output signal from essentially sinusoidal output signals of the receiving coils that is linearly related to positions of the rotor element. Additionally, a very simple evaluation process is provided, with which an angle sensor structured according to the invention functions. In this process, as high a degree of measuring accuracy as possible is achieved, and measuring inaccuracies due to component tolerances of the angle sensor are largely offset, or compensated.
According to principles of this invention, an evaluation circuit of an inductive angle sensor of the type described in the opening paragraph above has a selection device that selects at least one of output signals of receiving coils depending on momentary values of these output signals, and wherein the evaluation circuit determines a momentary position of a rotor element from a value of the at least one output signal.
As previously indicated, a change in position of the rotor element generates output signals in the receiving coils, the values of which (e.g. voltage values) substantially-sinusoidally depend on the position of the rotor element. In order to establish a linear inter-relationship between the position of the rotor element and a sensor output signal in a simple manner, an evaluation circuit of an angle sensor of this invention utilizes a nearly linear range about a zero crossing of a respective sine-wave function for evaluation purposes.
Since several receiving coils are provided that are offset with respect to each other by a predetermined angle, the evaluation circuit has a selection device that respectively selects output signals of receiving coils that are passing through the range of the zero crossing of the sine-wave function at that time.
A total measuring range of the angle sensor according to the invention is thus subdivided into several equal measuring sections, in each of which the output signal changes nearly linearly between a lower signal value and an upper signal value.
In such a process, the lower and upper signal values are the same for each measuring section so that, advantageously, elements of the evaluation circuit, specifically an analog digital converter provided for evaluation, can be structured precisely for that range of output signals.